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    activates ElectroMagnetic FLUKA: transport of electrons, positrons and


     WHAT(1-6): not used

: EMF-OFF to switch off electron and photon transport. Useful with the new defaults where EMF is on by default.
: EMF on
(option EMF not requested): if option DEFAULTS is not used, or if it is used with
= NEW-DEFAults, CALORIMEtry, EM-CASCAde, HADROTHErapy, ICARUS or PRECISIOn, electrons, positrons and photons are transported. If DEFAULTS is used with
= EET/TRANsmut, NEUTRONS, SHIELDINg or anything else, electrons, positrons and photons are not transported (see Note 2). To avoid their energy to be deposited at the point of production, it is generally recommended to discard those particles (see Note 5).
1) Option EMF is used to request a detailed transport of electrons, positrons and photons. Even if the primary particles are not photons or electrons, photons are created in high-energy hadron cascades, mainly as a product of pi0 decay, but also during evaporation and fission of excited nuclei; and capture gamma-rays are generated during low-energy neutrons transport. Electrons can arise from muon decay or can be set in motion in knock-on collisions by charged particles (delta-rays). 2) If EMF has been turned off by overriding the default (by setting
= EMF-OFF or by a DEFAULTS option which switches off electron-photon transport, such as OLD-DEFAults, EET/TRANsmut, NEUTRONS, SHIELDINg, not accompanied by an explicit EMF request), such electrons, positrons and photons are not transported and their energy is deposited on the spot at the point of creation unless those particles are DISCARDed (see Note 5 below). 3) Of course, it is also mandatory to request option EMF (either explicitly or implicitly via option DEFAULTS) in any pure electron, positron or photon problem (i.e. with electrons, positrons or photons as primary particles). 4) Using EMF without any biasing can lead to very large computing times, especially in problems of high primary energy or with low energy cutoffs. See in particular leading-particle biasing with EMF-BIAS. 5) In case of a pure hadron or neutron problem (e.g. neutron activation calculation) it is recommended to DISCARD electrons, positrons and photons (id-number 3, 4 and 7). In this case it is irrelevant whether the EMF card is present or not. Discarding only electrons and positrons, but not photons, may also be useful in some cases (for instance when calculating photon streaming in a duct). 6) An alternative is to set very large energy cutoffs for electrons and positrons (see EMFCUT). That will result in the electron energy being deposited at the point of photon interaction (kerma approximation, often sufficient for transport of photons having an energy lower than a few MeV). 7) Hadron photoproduction is dealt with by option PHOTONUC.
* This command must be issued without any WHAT parameter.

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